Synthesis and conformational behavior of pseudopeptides containing delta-azaproline. A cis conformational preference for Xaa(1)-delta-azaPro bond
Abstract
delta-Azaproline, a new bis-nitrogen proline surrogate has been used in order to control the conformation of an AA-Psi Pro bond. Conformational analysis of Xaa(1)-delta-azaPro-Xaa(3) performed by NMR, IR experiments, and molecular modeling revealed a preference for a trans conformation of the Xaa(1)-delta-azaPro bond when delta-azaPro is protected by a Boc group. The removal of the Boc protection leads to the establishment of a C-10 pseudocycle via a hydrogen bond network favoring the cis conformation of the Xaa(1)-delta-azaPro bond.